The invention relates to methods for welding tubular members in general and particularly to a method of butt welding a pair of vertically disposed ferrous tubular members having a wall thickness of more than 12 mm in end-to-end relationship by multi-pass gas-shielded arc welding with a consumable electrode from the outside of the tubular members without using a backing member.
When drilling wells e.g. offshore wells, vertically disposed tubes of substantial length are used to prevent materials as water, soil etc. to be introduced into the well and to remove other materials as oil from the drill hole.
The tube inserted into a drill hole consists of short tube sections welded together on site in end-to-end relationship. Until now manual welding methods were predominant requiring much time and high-qualified workers. However, the manually made welds are not of uniform quality. Therefore great efforts have been made to automate the welding operation which is a requirement for a perfect weld.
It has been proposed to improve the weld quality by preparing the opposed edges of the tube sections in a special manner before welding. Accordingly, the edge of the upper tube is beveled forming a conical surface inclined inwardly and downwardly at a bevel angle of appr. 45.degree. to the tube axis. The lower tube has a square edge or is beveled, thereby forming a conical surface inclined inwardly at a bevel angle of appr. 15.degree.. No root face is provided. The alignment of the two tubes is facilitated by the use of a backing member on the inner surface of the tubes. The backing member is welded together with the tubes and forms an integral part of the weld, thereby diminishing the inner section area of the tube. Submerged arc welding is used to join the tubes.
Disadvantages of the known welding methods are high costs, poor quality, binding defects at the flanks of the groove and the root, and poor dimensional accuracy of the inner section area of the tube near the weld.